Heater with simultaneous hot spot and mechanical intrusion protection

Abstract

An electrical heater utilizes negative temperature coefficient material (NTC) and current imbalance between live and neutral ends of the heater to simultaneously protect the heater from the hot spot and mechanical intrusion into the heating cable. The NTC layer, separating the heating wire and current leakage conductor, becomes electrically conductive at the temperatures above 60° C., thus “leaking” the current to earth. The hot spot is detected by measuring the current imbalance between line and neutral connections of the heating cable. The mechanical intrusion into the heater, such as cable or insulation damage, water or sharp metal object penetration, is also simultaneously measured by the same current imbalance measuring system such as Ground Fault Circuit Interrupter (GFCI). The optional return conductor and metal foil/mesh hot spot detection shields cancel electromagnetic field. The heater may contain positive temperature coefficient (PTC) continuous sensor to control the temperature in the heater. Such PTC sensor can be made of electrically conductive fibers and/or metal wires.

1. A heater having a durable construction for incorporation into a plurality of articles, said heater comprising:
 at least one continuous heating means, 
 at least one continuous current leakage conductor, 
 at least one continuous NTC sensing means, placed between, and electrically connected to said heating means and said current leakage conductor, said NTC sensing means provides current leakage between said heating means and said current leakage conductor; 
 at least one controller, for simultaneous protection from hot spot and mechanical intrusion into said heater, said hot spot is detected by measuring the imbalance of electrical current flowing between live and neutral ends of the electrical circuit of said heating means. 
 
   
   
     2. A heater as defined in  claim 1  further including at least one insulation means covering at least one side of combination of said heating means, said NTC sensing means and said current leakage conductor. 
   
   
     3. A heater as defined in  claim 1  wherein said current leakage conductor is electrically connected to the ground. 
   
   
     4. A heater as defined in  claim 1  wherein said current leakage conductor is electrically connected to one of the current supply conductors of said controller. 
   
   
     5. A heater as defined in  claim 1  further including sensing means. 
   
   
     6. A heater as defined in  claim 5  wherein said sensing means comprises PTC temperature sensing means with PTC detector. 
   
   
     7. A heater as defined in  claim 1  wherein said at least one NTC sensing means, placed between, and electrically connected to a return conductor and said current leakage conductor. 
   
   
     8. A heater as defined in  claim 1  wherein said heating means comprise a melting fuse, said melting fuse comprising at least one electrically conductive textile fiber as a heating means, said at least one electrically conductive textile fiber melts at a temperature above 110° C. and below 350° C. terminating electrical continuity in said heating means and preventing a fire hazard in said heating cable. 
   
   
     9. A heater as defined by  claim 1 , further including a visual indicator warning of hot spot on said controller. 
   
   
     10. The heater as defined by  claim 1 , further including sound signal warning of hot spot in said heater. 
   
   
     11. A method of simultaneous protection by a controller from a hot spot and mechanical intrusion into said heater, recited in  claim 1  comprises steps of:
 leaking of electrical current between said heating means and said current leakage conductor, through said NTC sensing means, 
 detecting an imbalance of electrical current flowing between live and neutral ends of the electrical circuit of said heating means, 
 terminating of electrical continuity in said heater upon reaching predetermined current leakage limiting setting. 
 
   
   
     12. A method of simultaneous protection by a controller as defined by  claim 11 , wherein said controller has separate said current leakage limiting settings for said hot spot and said mechanical intrusion in said heater. 
   
   
     13. A method of simultaneous protection by a controller as defined by  claim 12 , wherein the hot spot current leakage limiting setting is lower than mechanical intrusion current leakage limiting setting. 
   
   
     14. A method of simultaneous protection by a controller as defined by  claim 11 , wherein said heater further comprising PTC temperature sensing means and PTC detector to control the maximum heating level in said heater. 
   
   
     15. A method of simultaneous protection by a controller as defined by  claim 11 , further including a visual indicator warning of hot spot on said controller. 
   
   
     16. A method of simultaneous protection by a controller as defined by  claim 11 , further including sound signal warning of hot spot in said heater. 
   
   
     17. A method of simultaneous protection by a controller as defined by  claim 11  wherein said current leakage conductor is electrically connected to the ground. 
   
   
     18. A method of simultaneous protection by a controller as defined by  claim 11  wherein said current leakage conductor is electrically connected to one of the current supply conductors of said controller. 
   
   
     19. A method of simultaneous protection by a controller as defined by  claim 11 , wherein said controller comprises ground fault circuit interrupter.